1999 Dodge Neon boiling problems

Ok. My car has new radiator hoses, new thermostat, and just flushed the system out.

ok my car runs ok, but when I turn it off the water res starts to boil as well as the hoses. Like there is some blockage. I was told my head could be cracked or my block could be cracked as well. Well I was told to use block sealer, which we did and let the car sit up the 24 hrs it requires for the stuff to work. Well its boiling 3 times worse than before.

the water pump is working fine because you can see the water moving.

the only thing I can think of its the water res cap is missing and my radiator might need to be flushed out but even my mec. Is lost. He said it couldnt cause it to get that hot. Because it gets so hot you can smell the water and antifreeze. And you can hear it sizzle against the motor. ! Help please. I hope it dont need a new motor, because the motor runs fine there is not water in my oil or anything. And my head gasket isnt busted either because its blowing out like its supoose to out of the tail pipe.